Polycrystalline silicon may be prepared using a chemical vapor deposition (CVD) process in a cold wall bell jar reactor. Typically, this process is produced by CVD of a high purity silane or chlorosilane onto a heated substrate. The resulting product is a polycrystalline silicon workpiece such as a rod or ribbon. Polycrystalline silicon may be used to form monocrystalline silicon. Most semiconductor chips used in electronic devices are fabricated from monocrystalline silicon prepared by a Czochralski-type (CZ) process. In the CZ process, a monocrystalline silicon ingot is produced by melting polycrystalline silicon source material in a quartz crucible, stabilizing the crucible and source melt at an equilibrium temperature, dipping a seed crystal into the source melt, withdrawing the seed crystal as the source melt crystallizes on the seed to form a single crystal ingot, and pulling the ingot as it grows. Melting occurs at a temperature of 1412° C. to 1420° C. in an inert gas environment at low absolute pressure. The crucible is continually rotated about a generally vertical axis as the crystal grows. The rate at which the ingot is pulled from the source melt is selected to form an ingot having a desired diameter.
However, polycrystalline silicon workpieces are usually processed before they may be used to form monocrystalline silicon in the CZ process. The polycrystalline silicon workpieces are usually broken into pieces suitably sized for loading in the crucible. Mixtures of silicon pieces with different size distributions may be used to maximize the charge loaded in the crucible.
One method by which polycrystalline silicon workpieces are processed is a hand processing method. Operators in a clean room environment place the polycrystalline silicon workpieces on a low-contaminate work surface and strike the polycrystalline silicon workpieces with a low contamination impact tool to form polycrystalline silicon pieces.
The operators then manually sort the polycrystalline silicon pieces into at least two size distributions and package the sorted polycrystalline silicon pieces into high-purity bags. This process suffers from the drawbacks of being labor intensive and costly. Furthermore, this process suffers from the drawback that each operator may break and sort pieces somewhat differently, so the resulting product may differ in size distribution from operator to operator. Therefore, there is a continuing need for improved methods for preparing and sorting polycrystalline silicon pieces.